BIHANG TILL K. SV. VET.-AKAD. HANDL. BAND 27. AFD. IT. N:0 4. 7 



of the body, wliile the more adnlt ones present higher per- 

 cent-figures. In the same manner in the group of typical 

 reticulatus at the length of the body of 120 — 130 mm., be- 

 tween the younger and older individuals there is a marked 

 difference in the relative length of the upper jaw. In the 

 formseries (see Table IV, h/a and Jc/a) this onto-genetic pro- 

 gression is expressed by the almost unbroken series of in- 

 ereasing average-figiires for the six forms, counted from 

 f/racilis to reticulatus. This being the case, when seeing these 

 differences growing on with the natural development, we may 

 not expect here-in to find any constant specific characters, 

 as it rather seems probable that the respective forms are 

 only different stages of development of one and the same 

 species, but there are marked differences in the age, at which 

 the one and the other form acquires the same degree of de- 

 velopment. Thns f. i. the length of the nose (e) would give 

 a constant character (eui % < 6.3) for the forma gracilis (see 

 Table II), if it not were that the larval stage {a < 60 mm.) 

 of the typical Vahlii (Table II) as well as of frigidus (Table 

 III) presents almost the same figures as those of gracilis 

 when about 200 mm. long. Furthermore such a short nose 

 (ca%<7) reappears as individual abnormities in the whole 

 Vahlii-gYovq). 



With the changes of the length of the head follow in 

 general the changes of the distances from the tip of the nose 

 resp. to the beginning of the vertical fins (w and u) and to 

 the ventral fins (>■), the relative increase of the first-named 

 length taking with it a corresponding increase of these dis- 

 tances. Thns we may not expect in these relations to find 

 any constant characters for the different forms; but the above- 

 named sexual difference (?> o^ > 6 $), although not constant, 

 takes a more palpable expression in the relation between the 

 length of the head (6) and the distance from the tip of the 

 nose to the beginning of the anal fin (^^); thus in average: 



